1. Field of the Invention
The present invention generally relates to a dye-sensitized solar cell and, more particularly, to a dye-sensitized solar cell including a photoelectrode with three layers of nanostructure of different types and a method for producing the photoelectrode.
2. Description of the Related Art
Dye-sensitized solar cells have advantages such as low material cost and simple manufacturing process. Furthermore, dye-sensitized solar cells are flexible and light-permeable and contain multiple colors after formation. Due to the above advantages, dye-sensitized solar cells show enormous business potential and have been widely used in most of industries in recent years.
A dye-sensitized solar cell is mainly composed of a transparent conductive board, a photoelectrode, a dye, an electrolyte and a counter electrode. The dye is absorbed by the photoelectrode. Electrons are excited after the dye absorbs photons. The electrons are injected into a conduction band of the photoelectrode during a transfer process. The photoelectrode becomes charged and produces electricity during the transfer of the electrons. Therefore, the electron transfer rate between the photoelectrode and the dye is an important factor to the photoelectric conversion efficiency of the dye-sensitized solar cells. In light of this, it has been an important goal to improve the photoelectrode in the industry.
Taiwan Utility Model No. M403755 discloses a titanium dioxide photoanode with multiple layers of nanoscale thin films for a dye-sensitized solar ell. A hydrothermal process and arc process are used to produce the multilayer titanium dioxide photoanode with different types of nanoparticles (H200, Tnt-C550, and SF) to improve the light absorption efficiency of the photoanode as well as increasing the photoelectric conversion efficiency of the dye sensitized solar cell. The H200 nanoparticles have an average diameter of 20 nm, the Tnt-C550 nanoparticles have an average diameter of 25 nm, and the SF nanoparticles are in the form of needles and have an average diameter of 35 nm.
Although the light absorption effect of the conventional photoanode can be improved by the multiple layers of thin films, the conventional single film is simply replaced by the H200, Tnt-C550 and SF nanoparticles to properly adjust the light absorption and scattering effects via the differences in diameter of the nanoparticles among individual layers. However, each of the H200, Tnt-C550, and SF layers does not provide any other function, and the improvement of light absorption and scattering is limited. Even if the light absorption effect is improved, the electrons transfer rate in the photoanode can not be increased. Thus, the photoanode can not provide significant improvement in the photoelectric conversion efficiency.
Furthermore, in addition to the hydrothermal process and arc process for producing Tnt-C550 nanoparticles and H200 nanoparticles, vacuum submerged arc process is required to produce SF nanoparticles in the approach of using three different nanoparticles to form the photoanode. The processing procedures of the hydrothermal process and the vacuum submersed arc process are complicated and time-consuming, not allowing continuous mass production. Furthermore, the fitness between the Tnt-C550 nanoparticles, H200 nanoparticles, and SF nanoparticles could be adversely affected by uneven contact surfaces due to different diameters while stacking these particles to form the thin films. The quality of the resultant photoanode and the photoelectric conversion efficiency are, thus, not good.
Thus, a need exists for a novel photoelectrode for use in a dye-sensitized solar cell to solve the above problems.